Hey doob so I've had the exact same problem, premature pistil discoloration and I've heard several possible factors, humidity(or vpd)., high temperatures, and various nutrient problems like excessive phosphorus too early in flowering stage or in the vegetative stage. The podcast i listen to kis organics cannabis cultivation and science podcast had a big cultivator mention that broad/russet mites can also be a very big contributor to this...however they are sort of hard to spot and are often mistaken for overwatering, deficiencies and heat.
I've kind of just ended up watching the plant closely for excessive damage and taking it easy on the nutrients. I think you'll make it to harvest just fine but its always nice to try and find the problem.
Happy growing. ✌️